Powered vehicle seat height adjustors are typically actuated by a simple switch, which is undeniably simple, compact, and easy for a seat occupant to operate. However, the expense of powered systems is such that there is a continued interest in manually operable systems. In a manually operable seat height adjustor, there is the need for some kind of mechanical actuator, which generally takes the form of a lever that is grasped by the operator and rotated or lifted from an inoperative to an operative position. Clearly, as with any lever, the ease with which such an actuator may be operated is directly proportional to its length, the longer being the easier to operate. Conversely, its compactness suffers with increased length. A long lever rigidly joined to one element of a linkage would move that element of the linkage easily, but would likely, at least some point in its path of travel, extend above the level of the seat or otherwise extend into an undesired space in the interior of the vehicle. Consequently, such lever actuators are typically quite short, or are limited as to how far they rotate up or down.
A further shortcoming of many manual seat height adjustors is that the lever actuator, whatever its length, does no more than unlock a linkage that has a counterbalancing spring in it. Then it is up to the seat occupant to shift his or her weight up or down with the help only of the counterbalancing spring. The actuating lever is not held to any part of the linkage so that its mechanical advantage, however small it might be, can be used to assist in shifting the seat up or down. There is a known type of seat adjustor in which a telescoping handle is pulled out and rotated up or down, so as to be long when in use, but shorter and out of the way when not in use. This actuator also has a clutch spring that wraps a shaft of the linkage so that the mechanical advantage of the lever can be used by the operator seat occupant to assist in shifting up or down. There are limitations, however, to how rigidly a wrapping clutch spring can hold the shaft, and the stiffness of a telescoping tube is limited to the amount of metal overlap at the joint between its sections.